The invention relates to improvements in methods and apparatus for making rod-shaped smokers' articles (such as plain cigarettes or filter cigarettes) with dense ends.
Cigarettes with dense ends are normally produced by forming a continuous stream of fibrous material in a cigarette maker and densifying the stream at uniformly spaced locations prior or during draping of a web of cigarette paper therearound. The thus obtained cigarette rod is then severed across the densified portions and the resulting plain cigarettes are normally tested for the quality of their ends. It is customary to densify both ends of a plain cigarette or to densify the tobacco-containing ends of filter cigarettes so as to reduce the likelihood of escape of tobacco particles at the ends.
As a rule, or at least in many instances, the cigarette rod wherein the filter contains equidistant densified portions is severed midway across each densified portion. This ensures that the thus obtained halves of each densified portion are identical, or at least similar, as regards their length and other characteristics.
In accordance with a prior proposal, attempts to ensure the severing of a cigarette rod midway across the densified portions include accurate synchronization of operation of the trimming device (which removes the surplus from the tobacco stream) with that of the severing device (known as cutoff). Reference may be had to U.S. Pat. No. 3,604,430. The trimming device has one or more rotary disc-shaped surplus removing or trimming members with peripheral pockets which serve to prevent removal of the surplus in the regions of future densified portions of the filler. In order to correct the operation of the machine (if the tests indicate that the density of cigarette ends is unsatisfactory because the cigarette rod is not severed midway across the densified portions of its filler), the angular position of the rotary disc-shaped trimming member or members is changed to thus alter the positions of densified portions with reference to the cutting plane which is defined by the cutoff. The monitoring operation is carried out upon the cigarette rod, i.e., prior to subdivision of the rod into discrete rod-shaped articles of unit length or multiple unit length. This is not entirely satisfactory because additional departures from satisfactory operation can develop between the monitoring station and the cutoff. In other words, the monitoring of densified portions of the stream is premature so that the just discussed method and apparatus cannot invariably ensure that all defects in the making of cigarettes or other rod-shaped smokers' articles with dense ends can be remedied by the expedient of changing the angular position or positions of one or more rotary disc-shaped trimming members.
A further presently known mode of making rod-shaped smokers' articles with dense ends is disclosed in commonly owned copending patent application Ser. No. 899,348 filed Aug. 22, 1986 by Uwe Heitmann for "Apparatus for making cigarettes with dense ends", now U.S. Pat. No. 4,729,386 granted Mar. 8, 1988.